Medium detection mechanism and image forming device

ABSTRACT

The image forming device includes a recording paper setting plate on which media are set, a paper end sensor lever, and a print control section that controls the whole of the device. The paper end sensor lever includes a paper contact part for detecting a first condition in which there are no media set on the recording paper setting plate and an arm contact part for detecting a second condition in which the amount of the media set on the recording paper setting plate is smaller than a prescribed amount.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a medium detection mechanism that detects the amount of media set in a medium setting part, and to an image forming device including the medium detection mechanism.

2. Description of the Related Art

Conventionally, there are devices that convey a medium that has been set in a medium setting part and perform image formation on the conveyed medium. Among such devices, there exist devices that enhance the user convenience by displaying a condition such as the amount of media set in the medium setting part. Japanese Patent Application Publication No. 2015-127250 describes a medium conveyance device including a paper detection section.

However, there are cases where it is required to detect the amount of the media set in the medium setting part with a simple structure.

SUMMARY OF THE INVENTION

The object of the present invention, which has been made to resolve the above-described problem, is to detect the amount of the media set in the medium setting part with a simple structure.

A medium detection mechanism according to an aspect of the present invention includes a medium setting part in which media are set; a rotating member having a rotational central shaft, the rotating member being configured to rotate around the rotational central shaft depending on an amount of the media set in the medium setting part; a detection sensor that detects the rotation of the rotating member; a display section that displays a condition of the medium detection mechanism; and a control section that controls the display section. The rotating member includes a first arm part for detecting a first condition in which there are no media set in the medium setting part and a second arm part for detecting a second condition in which the amount of the media set in the medium setting part is smaller than a prescribed amount, and the control section makes a first display indicating that there are no media set in the medium setting part on the display section when the media are judged to be in the first condition based on result of the detection by the detection sensor and makes a second display indicating that the amount of the media set in the medium setting part is smaller than the prescribed amount on the display section when the media are judged to be in the second condition based on the result of the detection by the detection sensor.

An image forming device according to another aspect of the present invention includes the above-described medium detection mechanism.

According to the present invention, the amount of the media set in the medium setting part can be detected with a simple structure.

BRIEF DESCRIPTION OF THE DRAWINGS

In the attached drawings,

FIG. 1 is a side view showing the general configuration of an image forming device according to a first embodiment;

FIG. 2 is a perspective view showing the general configuration of the image forming device according to the first embodiment;

FIG. 3 is a functional block diagram showing the general configuration of the image forming device according to the first embodiment;

FIG. 4A is an exploded perspective view showing the general configuration of a sheet feed storage cassette in the first embodiment, and FIG. 4B is a partially enlarged view of FIG. 4A;

FIG. 5A is a side view showing the general configuration of the sheet feed storage cassette in the first embodiment, wherein the sheet feed storage cassette in a state before insertion is shown;

FIG. 5B is a partially enlarged view of a paper remaining amount detection section in the sheet feed storage cassette shown in FIG. 5A;

FIG. 6A is a side view showing the general configuration of the sheet feed storage cassette in the first embodiment, wherein the sheet feed storage cassette in an inserted state is shown;

FIG. 6B is a partially enlarged view of the paper remaining amount detection section in the sheet feed storage cassette shown in FIG. 6A;

FIG. 7A is a side view showing the general configuration of the sheet feed storage cassette in the first embodiment, showing a state at a time when a near end condition of recording paper is detected;

FIG. 7B is a partially enlarged view of the paper remaining amount detection section in the sheet feed storage cassette shown in FIG. 7A;

FIG. 8A is a side view showing the general configuration of the sheet feed storage cassette in the first embodiment, showing a state at a time when a paper end condition of the recording paper is detected;

FIG. 8B is a partially enlarged view of the paper remaining amount detection section in the sheet feed storage cassette shown in FIG. 8A;

FIG. 9 is a flowchart showing an operation for making a condition check of the recording paper in the first embodiment;

FIG. 10 is a diagram showing the relationship between the thickness of the recording paper and a corrective number of sheets used for correcting the timing of near end display in the first embodiment;

FIG. 11A is a side view showing the general configuration of a sheet feed storage cassette in a second embodiment, showing a state where preliminary detection is made;

FIG. 11B is a partially enlarged view of a paper remaining amount detection section in the sheet feed storage cassette shown in FIG. 11A;

FIG. 12A is a partially enlarged view of a paper remaining amount detection section in the second embodiment, showing a state after the preliminary detection and before the near end condition is detected;

FIG. 12B is a partially enlarged view of the paper remaining amount detection section in the second embodiment, showing a state at a time when the near end condition is detected;

FIG. 12C is a partially enlarged view of the paper remaining amount detection section in the second embodiment, showing a state at a time when the paper end condition is detected;

FIG. 13A is a time chart showing an example of near end detection in the second embodiment, and FIG. 13B is a time chart showing another example of the near end detection in the second embodiment;

FIG. 14A is an enlarged view showing the general configuration of a paper remaining amount detection section in a third embodiment, showing a state at a time when a paper sufficiency condition is detected;

FIG. 14B is an enlarged view showing the general configuration of the paper remaining amount detection section in the third embodiment, showing a state at a time of the preliminary detection;

FIG. 14C is an enlarged view showing the general configuration of the paper remaining amount detection section in the third embodiment, showing a state after the preliminary detection and before detecting the near end condition;

FIG. 14D is an enlarged view showing the general configuration of the paper remaining amount detection section in the third embodiment, showing a state at a time when the near end condition is detected;

FIG. 14E is an enlarged view showing the general configuration of the paper remaining amount detection section in the third embodiment, showing a state at a time when the paper end condition is detected;

FIG. 15 is a flowchart showing an operation for near end detection restoration in the third embodiment; and

FIG. 16 is a table showing the relationship between an output of a density sensor and a display on a display panel in the third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications will become apparent to those skilled in the art from the detailed description.

An image forming device according to an embodiment of the present invention will be described below with reference to the accompanying drawings. The image forming device according to the embodiment is a device including a medium detection mechanism that detects the amount of media that have been set in the image forming device. In the following description, a configuration that detects the amount of the media that have been set in the image forming device will be referred to as the medium detection mechanism.

An xyz orthogonal coordinate system is shown in the drawings to facilitate the understanding of the relationship among the drawings. An x-axis in the drawings is shown as a coordinate axis in an axial direction parallel to a width direction of the image forming device. A y-axis in the drawings is shown as a coordinate axis in an axial direction parallel to a depth direction of the image forming device. A z-axis in the drawings is shown as a coordinate axis orthogonal to both the x-axis and the y-axis and parallel to a vertical direction of the image forming device.

In the following description, a paper end condition as a first condition means a condition in which the remaining amount of paper is zero, a near end condition as a second condition means a condition in which the remaining amount of the paper is small (smaller than a prescribed amount), and a paper sufficiency condition as a third condition means a condition in which the remaining amount of the paper is sufficient (larger than or equal to the prescribed amount).

(1) First Embodiment (1-1) Configuration

The configuration of an image forming device 100 according to a first embodiment of the present invention will be described below with reference to FIG. 1 to FIG. 5. FIG. 1 is a side view showing the general configuration of the image forming device 100 according to the first embodiment. FIG. 2 is a perspective view showing the general configuration of the image forming device 100 according to the first embodiment.

The image forming device 100 conveys recording paper (sheet of paper) along a sheet conveyance path formed substantially in an S-shape and extending from a sheet feed storage cassette 230 as a starting point to a recording paper stack part 210 as an end point. As shown in FIG. 1, the image forming device 100 includes a recording paper setting plate 104 as a medium setting part, a recording paper setting plate fulcrum 105, a spring 106 as an elastic part, recording paper 201, a recording paper feed roller 202 as a medium conveyance part, first registration rollers 203, second registration rollers 204, an image forming section 205, a fixation unit 206, first ejection rollers 207, second ejection rollers 208, ejected recording paper 209, the recording paper stack part 210, a sheet feed tray 211, a paper end sensor 212, an IN sensor 213, a WR sensor 214, a recording paper conveyance roller 215, a recording paper separation roller 216, and the sheet feed storage cassette 230.

The sheet feed storage cassette 230, storing multiple sheets of recording paper 201 therein in a stacked state, is attached to a lower part of the image forming device 100 in a detachable manner. Provided over the sheet feed storage cassette 230 is the recording paper feed roller 202 that comes in contact with a sheet of recording paper 201 in the uppermost part of the stack of recording paper 201 stored in the sheet feed storage cassette 230 and sends out the recording paper 201 from the uppermost part. The recording paper 201 sent out by the recording paper feed roller 202 is separated from the stack by the recording paper conveyance roller 215 and the recording paper separation roller 216 provided as a pair of rollers and is conveyed as an individual sheet along the sheet conveyance path in a conveyance direction.

The recording paper setting plate 104 is a setting plate arranged in the sheet feed storage cassette 230 to set the stacked recording paper 201. Arranged under the recording paper setting plate 104 is the spring 106, by which the recording paper setting plate 104 is biased upward. The recording paper setting plate 104 is capable of tilting depending on the number of sheets of the recording paper 201 set on the recording paper setting plate 104 by using the recording paper setting plate fulcrum 105 as the fulcrum.

The recording paper setting plate 104 remains in a substantially horizontal state when the number of sheets of the recording paper 201 set on the recording paper setting plate 104 is large, and the tilt angle of the recording paper setting plate 104 increases with the decrease in the number of sheets of the recording paper 201 set on the recording paper setting plate 104. The tilting of the recording paper setting plate 104 enables the uppermost part of the stacked recording paper 201 to come in contact with the recording paper feed roller 202 even when the number of sheets of the recording paper 201 set on the recording paper setting plate 104 has decreased. Accordingly, the sheet conveyance is carried out appropriately.

As shown in FIG. 1, the paper end sensor 212 that detects the position of top layer recording paper 201 in the stacked recording paper 201 is placed at the top of the recording paper 201 stacked in the sheet feed storage cassette 230. The paper end sensor 212 detects the condition in which there is no recording paper 201 stacked in the sheet feed storage cassette 230 (paper end condition). As well as detecting the paper end condition of the recording paper 201, the paper end sensor 212 in the first embodiment is capable of detecting the condition in which the amount of the recording paper 201 stacked in the sheet feed storage cassette 230 is small (near end condition) and the condition in which the amount of the recording paper 201 is larger than or equal to the prescribed amount (paper sufficiency condition).

The first registration rollers 203 are roller members formed of rubber material such as ethylene propylene diene rubber or urethane rubber, for example, and supported by rotary shafts that are not illustrated. The first registration rollers 203 correct the skew of the recording paper 201 (oblique feeding of the sheet) by using collision of the recording paper 201 with the rollers in the stopped state.

The second registration rollers 204 are roller members formed of rubber material such as ethylene propylene diene rubber or urethane rubber, for example, and supported by rotary shafts that is not illustrated. The second registration rollers 204 convey the recording paper 201 after the skew correction by the first registration rollers 203 to a transfer belt of the image forming section 205.

As shown in FIG. 1, the IN sensor 213 is arranged between the first registration rollers 203 and the second registration rollers 204 along the sheet conveyance path. Further, the WR sensor 214 is arranged between the second registration rollers 204 and the image forming section 205. The IN sensor 213 is a sensor that detects conveyance of the recording paper 201 thereto through the conveyance path. The WR sensor 214 is a sensor that detects the conveyed recording paper 201 at a position in front of the image forming section 205 in order to determine write timing of the image forming section 205.

In the image forming section 205, yellow, magenta, cyan and black image forming units are arranged in series along the conveyance path of the recording paper 201. Each of the image forming units includes a photosensitive drum as an electrostatic latent image bearing body for forming an image, a development device as a development section for developing an electrostatic latent image formed on the photosensitive drum by use of toner and thereby forming a toner image, and a toner cartridge for supplying the toner to the development device.

Each of the image forming units further includes a charging roller as a charging section for supplying electric charge to the surface of the photosensitive drum and thereby uniformly charging the surface. Moreover, each of the image forming units includes an LED head as an exposure device for irradiating the uniformly charged surface of the photosensitive drum with light according to image data and thereby forming the electrostatic latent image.

The image forming section 205 further includes a transfer belt that conveys the recording paper 201 and transfer rollers as transfer sections. Each of the transfer rollers transfers the toner image, formed on the photosensitive drum by visualizing (developing) the electrostatic latent image with the toner, onto the recording paper 201. Each of the transfer rollers is arranged to face the corresponding photosensitive drum so that the transfer belt is sandwiched between the transfer roller and the photosensitive drum at a transfer position.

Further, in the image forming section 205, a cleaning blade for removing (scraping off) the toner remaining on the surface of the photosensitive drum after the transfer of the toner image onto the recording paper 201 is arranged in contact with the photosensitive drum.

As shown in FIG. 1, the fixation unit 206 is arranged in the sheet conveyance path on the downstream side of the image forming section 205 and includes a heat roller, a backup roller, and a thermistor or the like, for example. The heat roller is formed by, for example, coating a cylindrical hollow cored bar made of aluminum or the like with a heat-resistant elastic layer of silicone rubber and further coating the heat-resistant elastic layer with another member. In the cored bar, a heater such as a halogen lamp is provided, for example.

The backup roller is formed by, for example, coating a cored bar made of aluminum or the like with a heat-resistant elastic layer of silicone rubber and further coating the heat-resistant elastic layer with a PFA (polytetrafluoroethylene) tube, and is arranged so that a pressing part is formed between the backup roller and the heat roller. The heat roller and the backup roller rotate according to control by a fixation control section. The thermistor is a surface temperature detecting means for the heat roller and is arranged in the vicinity of the surface of the heat roller.

The recording paper 201 to which the toner images have been transferred passes through the pressing part formed by the backup roller and the heat roller maintained at a prescribed temperature, and thereby heat and pressure are applied to the toners on the recording paper 201, the toners are fused and the toner images are fixed on the recording paper 201.

The first ejection rollers 207 and the second ejection rollers 208 convey the recording paper 201 after passing through the fixation unit 206 along the sheet conveyance path and eject the recording paper 201 onto the recording paper stack part 210 formed by using the outer housing of the image forming device 100. As shown in FIG. 1, multiple sheets of the ejected recording paper 209 are loaded on the recording paper stack part 210.

As shown in FIG. 2, the image forming device 100 includes an operation panel 217 as an operation section of the image forming device, a display panel 218 for displaying operating status to a user, and operation keys 219 for receiving operations performed by the user. The operation panel 217, the display panel 218 and the operation keys 219 are formed at the top of the image forming device 100 as shown in FIG. 2.

FIG. 3 is a functional block diagram showing the general configuration of the image forming device 100 according to the first embodiment. As shown in FIG. 3, the image forming device 100 includes a print control section 222 as a control section. As shown in FIG. 3, the print control section 222 is connected to a sheet feed conveyance motor 232 as a drive source for the recording paper 201, a main motor 233 as a drive source for the image forming section 205, and a fixation motor 234 as a drive source for the fixation unit 206.

The print control section 222 controls the sheet feed conveyance motor 232 and thereby controls the rotation of the recording paper feed roller 202, the recording paper conveyance roller 215, the recording paper separation roller 216, the first registration rollers 203, the second registration rollers 204, the first ejection rollers 207 and the second ejection rollers 208. The print control section 222 controls the main motor 233 and thereby controls the print process. The print control section 222 controls the fixation motor 234 and thereby controls the fixation unit 206.

As shown in FIG. 3, the print control section 222 includes a print number counter 223 as a print number measurement section, a time counter 224 as a time measurement section, a medium setting storage section 225, and a paper remaining amount judgment section 226. A network (or external device) 231 is connected to the print control section 222. Further, various sensors (the IN sensor 213, the WR sensor 214 and the paper end sensor 212) and the operation panel 217 are connected to the print control section 222. The operation panel 217 includes the display panel 218 and the operation keys 219. The print control section 222 controls a display on the display panel 218.

The print number counter 223 counts the number of sheets on which the printing is performed in a prescribed time measured by the time counter 224. The medium setting storage section 225 stores information on the recording paper 201 stored in the sheet feed storage cassette 230 (e.g., thickness information on the recording paper 201). The paper remaining amount judgment section 226 makes a judgment on the remaining amount of the loaded recording paper 201.

Next, detailed structure of a paper remaining amount detection section 200 in the first embodiment will be described below with reference to FIGS. 4A and 4B and FIGS. 5A and 5B. The paper remaining amount detection section 200 is a mechanism for detecting the remaining amount of the recording paper 201 by using the paper end sensor 212 and other members. FIG. 4A is an exploded perspective view showing the general configuration of the sheet feed storage cassette 230 in the first embodiment, and FIG. 4B is a partially enlarged view of FIG. 4A. FIGS. 4A and 4B illustrate a state in which the sheet feed storage cassette 230 has not been inserted into the image forming device 100 yet (i.e., the sheet feed storage cassette 230 has been drawn out from the image forming device 100).

FIG. 5A is a side view showing the general configuration of the sheet feed storage cassette 230 in the first embodiment, wherein the sheet feed storage cassette 230 in a state before insertion is shown. FIG. 5B is a partially enlarged view of the paper remaining amount detection section 200 in the sheet feed storage cassette 230 shown in FIG. 5A.

As shown in FIGS. 4A and 4B, the sheet feed storage cassette 230 includes a recording paper side guide 227 that comes in contact with a side face of the recording paper 201. The sheet feed storage cassette 230 is inserted to a part under a base plate 228 of the image forming device 100 and the insertion of the sheet feed storage cassette 230 into the image forming device 100 is detected by a cassette presence/absence detection section 229. The recording paper setting plate 104, on which multiple sheets of recording paper 201 are stacked and set, is installed on the sheet feed storage cassette 230. As shown in FIG. 4A, an opening 125 is formed through the recording paper setting plate 104.

As shown in FIG. 5A, the sheet feed storage cassette 230 includes a drive mechanism that drives the recording paper setting plate 104 up and down. The drive mechanism includes a sun gear 107 as a gear part, a planet gear 108, an internal gear rack 109, a shaft 110, a torque damper 111, a ratchet gear 112, a lock lever 113, a lock spring 114, a one-way gear 115, a gear part cover 116, a detection projection part 117, and a detection arm part 119 as an intermediating member.

As shown in FIG. 5A, the recording paper setting plate 104 is connected to the shaft 110, and the planet gear 108 is fixed to each end of the shaft 110 in the x-axis direction. Further, the internal gear rack 109 is formed to engage with the planet gear 108. The planet gear 108 is capable of moving up and down along the internal gear rack 109.

As shown in FIG. 5A, the sun gear 107 is installed in the sheet feed storage cassette 230 to engage with the planet gear 108. Further, the ratchet gear 112 is installed on the same shaft as the sun gear 107. Furthermore, the one-way gear 115 is installed to engage with both the sun gear 107 and the ratchet gear 112. The torque damper 111 is installed to engage with the one-way gear 115.

As shown in FIG. 5A, the detection arm part (intermediating member) 119 is provided inside the sheet feed storage cassette 230. The detection arm part 119 is formed integrally with the gear part cover 116 shown in FIG. 4B. The sun gear 107 having the detection projection part 117 formed thereon rotates along with the rotation of the planet gear 108, and thereby the detection projection part 117 and the detection arm part 119 are brought into a contact state or a non-contact state.

As shown in FIG. 5A, the lock lever 113 that sets the ratchet gear 112 in a locked state by engaging with the ratchet gear 112 and the lock spring 114 that applies pressing force to the lock lever 113 are installed on the upper side of the ratchet gear 112. In the locked state, the left-hand side of the lock lever 113 is biased upward by the lock spring 114, while the right-hand side of the lock lever 113 is biased downward and thereby engaged with the ratchet gear 112 to keep the ratchet gear 112 in the locked state in which the ratchet gear 112 is prevented from rotating.

As shown in FIGS. 4A and 4B, the base plate 228 of the image forming device 100 is provided with a paper end sensor holder 126. The paper end sensor holder 126 is a holder that covers the whole of the paper end sensor 212. A photosensor 103 and a paper end sensor lever 102 as a rotating member are fixed inside the paper end sensor holder 126. The photosensor 103 as a detection sensor includes a light emission part and a light reception part and emits light from the light emission part in the x-axis direction in FIGS. 4A and 4B. The photosensor 103 has a function of detecting the rotation of the paper end sensor lever 102.

As shown in FIG. 5B, the paper end sensor lever 102 includes a shaft 102 a as a rotary central shaft, a paper contact part 124 as a first arm part that comes in contact with the top layer recording paper 201 in the sheet feed storage cassette 230, an arm contact part 123 as a second arm part that comes in contact with the detection arm part 119 of the sheet feed storage cassette 230, and a photosensor light blocking part 120.

The photosensor light blocking part 120 is a projecting part provided on the shaft 102 a of the paper end sensor lever 102. The photosensor light blocking part 120 rotates around the shaft 102 a of the paper end sensor lever 102 according to the remaining amount of the recording paper 201 set on the recording paper setting plate 104 detected by the paper end sensor lever 102 and thereby blocks or transmits the light from the photosensor 103.

As shown in FIG. 5B, the photosensor light blocking part 120 includes a photosensor transmissive part 120 a as a light transmissive part, and a first photosensor light blocking part 120 b and a second photosensor light blocking part 120 c as light blocking parts. The photosensor transmissive part 120 a is a void part of the photosensor light blocking part 120 and has a function of transmitting the light emitted from the photosensor 103 by coinciding with a photosensor optical axis 133 when the paper contact part 124 comes in contact with the recording paper 201. In a state in which the light emitted from the photosensor 103 passes through the photosensor transmissive part 120 a, the photosensor 103 is on and the paper sufficiency condition of the recording paper 201 is detected.

The first photosensor light blocking part 120 b is arranged to the left of the photosensor transmissive part 120 a in FIG. 5B and has a function of blocking the light emitted from the photosensor 103 when the contact of the paper contact part 124 and the recording paper 201 is released. By the blockage of the light emitted from the photosensor 103 by the first photosensor light blocking part 120 b, the photosensor 103 is turned off and the paper end condition of the recording paper 201 is detected.

The second photosensor light blocking part 120 c is arranged to the right of the photosensor transmissive part 120 a in FIG. 5B and has a function of blocking the light emitted from the photosensor 103 by rotating to a position coinciding with the photosensor optical axis 133 when the arm contact part 123 comes in contact with the detection arm part 119. By the blockage of the light emitted from the photosensor 103 by the second photosensor light blocking part 120 c, the photosensor 103 is turned off and the near end condition of the recording paper 201 is detected.

As shown in FIG. 5B, the base plate 228 is provided with a lock lever releasing part 134 that comes in contact with the lock lever 113 due to the insertion of the sheet feed storage cassette 230 into the image forming device 100 and thereby releases the locked state of the lock lever 113.

(1-2) Operation

Next, the flow of the print operation performed by the image forming device 100 according to the first embodiment will be described below. After a print command from the network (or external device) 231 is received by the print control section 222, the recording paper 201 set in the sheet feed storage cassette 230 is conveyed by making the sheet feed conveyance motor 232 rotate the recording paper feed roller 202.

The recording paper 201 after reaching the recording paper conveyance roller 215 is separated from the stack by the recording paper separation roller 216 and detected by the IN sensor 213, and thereafter the sheet feed conveyance motor 232 is stopped temporarily by a command from the print control section 222 in the state in which the recording paper 201 has collided with the second registration rollers 204.

Subsequently, the conveyance of the recording paper 201 is restarted by making the sheet feed conveyance motor 232 rotate the second registration rollers 204. The front end position of the recording paper 201 is detected by the print control section 222 by using the WR sensor 214, and the toners are transferred to the recording paper 201 by the image forming section 205 driven by the main motor 233 and performing the toner/latent image formation and the image transfer.

Subsequently, the toners are thermally fused and fixed on the recording paper 201 by the fixation unit 206 driven by the fixation motor 234. The recording paper 201 is conveyed by the first ejection rollers 207 and the second ejection rollers 208 and ejected onto the recording paper stack part 210, so that the print operation is ended.

Next, the operation of the paper remaining amount detection performed by the image forming device 100 according to the first embodiment will be described below with reference to FIGS. 5A and 5B to FIGS. 8A and 8B. The operation described below is an operation for making a condition check in regard to the number of sheets of the recording paper 201 stored in the sheet feed storage cassette 230 after the sheet feed storage cassette 230 is set in the image forming device 100.

FIG. 6A is a side view showing the general configuration of the sheet feed storage cassette 230 in the first embodiment, wherein the sheet feed storage cassette 230 in an inserted state is shown. FIG. 6B is a partially enlarged view of the paper remaining amount detection section 200 in the sheet feed storage cassette 230 shown in FIG. 6A. FIGS. 6A and 6B illustrate a case where a large amount of recording paper 201 has been loaded on the recording paper setting plate 104.

FIG. 7A is a side view showing the general configuration of the sheet feed storage cassette 230 in the first embodiment, showing a state at a time when the near end condition of the recording paper 201 is detected. FIG. 7B is a partially enlarged view of the paper remaining amount detection section 200 in the sheet feed storage cassette 230 shown in FIG. 7A. FIGS. 7A and 7B illustrate a case where the amount of the recording paper 201 loaded on the recording paper setting plate 104 is smaller than or equal to the prescribed amount.

FIG. 8A is a side view showing the general configuration of the sheet feed storage cassette 230 in the first embodiment, showing a state at a time when the paper end condition of the recording paper 201 is detected. FIG. 8B is a partially enlarged view of the paper remaining amount detection section 200 in the sheet feed storage cassette 230 shown in FIG. 8A. FIGS. 8A and 8B illustrate a case where the number of sheets of the recording paper 201 loaded on the recording paper setting plate 104 is zero.

As shown in FIGS. 5A and 5B, in the state before the sheet feed storage cassette 230 is inserted into the image forming device 100, the planet gear 108, the sun gear 107, the one-way gear 115 and the ratchet gear 112 are engaged with each other. Further, since the ratchet gear 112 and the lock lever 113 pressed by the lock spring 114 are engaged with each other, each of the connected gears is inhibited from rotating and is stopped at the illustrated position.

Further, as shown in FIGS. 5A and 5B, although the recording paper setting plate 104 in the sheet feed storage cassette 230 is pressed upward by the spring 106, the recording paper setting plate 104 connected to the planet gear 108 is locked up at its lowermost position since the gears are in the locked state. In this case, the photosensor 103 is in the off state since the photosensor transmissive part 120 a and the photosensor optical axis 133 do not coincide with each other and the light emitted from the photosensor 103 is blocked by the first photosensor light blocking part 120 b.

From the state shown in FIGS. 5A and 5B, the recording paper 201 is set on the recording paper setting plate 104 and the sheet feed storage cassette 230 is inserted into the image forming device 100 in a direction A. Then, the cassette presence/absence detection section 229 comes in contact with a non-illustrated detection switch in the image forming device 100 and detects the completion of the insertion of the sheet feed storage cassette 230. This state is shown in FIGS. 6A and 6B.

When the sheet feed storage cassette 230 is inserted in the image forming device 100 as shown in FIGS. 6A and 6B, the lock lever releasing part 134 and the lock lever 113 come in contact with each other, the lock lever 113 is depressed in a direction B, and the engagement with the ratchet gear 112 is released. Thereby, the recording paper setting plate 104 starts ascending together with the recording paper 201 due to pressing force applied from the spring 106.

The recording paper setting plate 104 stops ascending when the top layer of the recording paper 201 stacked on the recording paper setting plate 104 comes in contact with the recording paper feed roller 202. In this case, the top layer recording paper 201 and the paper contact part 124 come in contact with each other and the paper end sensor lever 102 rotates counterclockwise. At that time, the paper end sensor lever 102 has rotated to a third rotational position. In this case, the photosensor transmissive part 120 a and the photosensor optical axis 133 coincide with each other and the photosensor 103 turns on.

Here, the time from the start of the ascending of the recording paper setting plate 104 to the turning-on of the photosensor 103 is measured by the time counter 224 of the print control section 222. A time measured until the photosensor 103 turns on is defined as a time (measurement time) T. The time T is a rotation time of the planet gear 108 from the start of the ascending of the recording paper setting plate 104 to the stoppage of the ascending.

In a case where the time T is within a time T1 as a predetermined first time, it can be identified that the recording paper 201 and the paper contact part 124 have come in contact with each other and the paper end sensor lever 102 has rotated, and thus the paper remaining amount judgment section 226 of the print control section 222 judges that the recording paper 201 exists, and a display indicating that the printing is possible is made on the display panel 218.

When the amount of the recording paper 201 loaded on the recording paper setting plate 104 is smaller than or equal to the prescribed amount (near end condition) as shown in FIGS. 7A and 7B, the recording paper setting plate 104 has ascended further since the planet gear 108 rotationally moves further clockwise from the state shown in FIGS. 6A and 6B. In this case, first, the photosensor 103 turns on due to the contact of the paper contact part 124 and the recording paper 201. Subsequently, the sun gear 107 rotates together with the planet gear 108, and the detection projection part 117 formed on the sun gear 107 comes in contact with a projection part 119 a of the detection arm part 119 and thereby raises the detection arm part 119.

By the raising of the detection arm part 119, the arm contact part 123 of the paper end sensor lever 102 comes in contact with the detection arm part 119. The contact causes the paper end sensor lever 102 to rotate further counterclockwise from the state shown in FIGS. 6A and 6B. At that time, the paper end sensor lever 102 has rotated to a second rotational position. Due to the counterclockwise rotation of the paper end sensor lever 102, the photosensor transmissive part 120 a moves to a position not coinciding with the photosensor optical axis 133 and the photosensor 103 turns off. Therefore, the photosensor 103 temporarily turns on and thereafter turns off.

In this case, since a relationship T1<T<T2 holds among the measured time T, the aforementioned time T1 and a time T2 as a second time longer than the time T1 and the photosensor 103 temporarily turned on and thereafter turned off, the paper remaining amount judgment section 226 of the print control section 222 judges that the condition of the stacked recording paper 201 is the near end condition (in which the remaining amount of the paper is small) and a near end display is made on the display panel 218.

When the number of sheets of the recording paper 201 loaded on the recording paper setting plate 104 is zero (paper end condition) as shown in FIGS. 8A and 8B, the planet gear 108 has rotationally moved further upward from the state shown in FIGS. 7A and 7B. In this case, the sun gear 107 rotates further from the state shown in FIGS. 7A and 7B, the contact of the detection projection part 117 formed on the sun gear 107 with the projection part 119 a of the detection arm part 119 is lost, and the detection arm part 119 descends.

By the descending of the detection arm part 119, the contact of the arm contact part 123 and the detection arm part 119 is lost and the paper end sensor lever 102 rotates clockwise from the state shown in FIGS. 7A and 7B in this case. Here, the opening 125 is formed through the recording paper setting plate 104 at a position corresponding to the paper contact part 124. When the paper end sensor lever 102 in the state shown in FIGS. 7A and 7B has rotated clockwise to the state shown in FIGS. 8A and 8B, the recording paper 201 shielding the opening 125 has run out.

In this case, the paper contact part 124 never comes in contact with the recording paper setting plate 104 due to the opening 125, and thus the paper end sensor lever 102 rotates further clockwise compared to a case where there remains the recording paper 201, and rotates to a position where the first photosensor light blocking part 120 b blocks the light from the photosensor 103 as shown in FIG. 8B. In this case, the paper end sensor lever 102 is situated at a first rotational position and the photosensor 103 is off.

As above, since no recording paper 201 is set on the recording paper setting plate 104 in the paper end condition, the paper contact part 124 never comes in contact with the recording paper 201 and the photosensor 103 never turns on within the time T1 or the time T2 as in the aforementioned paper sufficiency condition or near end condition. Therefore, the photosensor 103 does not turn on within the time T2.

As above, based on the fact that the photosensor 103 does not turn on within the time T2, the paper remaining amount judgment section 226 of the print control section 222 judges that the condition of the stacked recording paper 201 is the paper end condition (in which the remaining amount of the paper is zero) and a paper end display is made on the display panel 218.

Next, an operation of paper remaining amount display performed by the image forming device 100 according to the first embodiment will be described below with reference to FIG. 9. FIG. 9 is a flowchart showing an operation for making the condition check in regard to the remaining amount of the recording paper 201 in the first embodiment. As shown in FIG. 9, the insertion of the sheet feed storage cassette 230 is detected by the cassette presence/absence detection section 229 in step S1.

In the next step S2, a judgment is made on whether or not the time T until the photosensor 103 turns on is within the predetermined time T1. In a case where the time T is within the time T1 (YES in the step S2), it can be identified that the recording paper 201 and the paper contact part 124 have come in contact with each other and the paper end sensor lever 102 has rotated, and thus the process advances to step S5, the paper remaining amount judgment section 226 of the print control section 222 judges that the recording paper 201 exists, and the display indicating that the printing is possible is made on the display panel 218.

In a case where the time T is longer than the time T1 in the step S2 (NO in the step S2), the process advances to the next step S3 and a judgment is made on whether or not the photosensor 103 temporarily turned on within the time T2 and thereafter turned off since there is possibility that the photosensor 103 temporarily turned on within the time T2 and thereafter turned off.

In a case where the photosensor 103 temporarily turned on within the time T2 and thereafter turned off in the step S3 (YES in the step S3), it can be identified that the paper end sensor lever 102 has rotated counterclockwise due to the contact of the detection arm part 119 with the arm contact part 123 of the paper end sensor lever 102 and the photosensor 103 has turned off, and thus the process advances to step S6, the paper remaining amount judgment section 226 of the print control section 222 judges that the condition of the stacked recording paper 201 is the near end condition (in which the remaining amount of the paper is small), and the near end display is made on the display panel 218.

In a case where the photosensor 103 did not temporarily turn on within the time T2 in the step S3 (NO in the step S3), it can be identified that there remains no recording paper 201 set on the recording paper setting plate 104, and thus the process advances to step S4, the paper remaining amount judgment section 226 of the print control section 222 judges that the condition of the stacked recording paper 201 is the paper end condition (in which the remaining amount of the paper is zero), and the paper end display is made on the display panel 218. The operation for making the condition check in regard to the insertion of the sheet feed storage cassette 230 and the remaining amount of the recording paper 201 is completed as above.

Next, processing after the start of the printing will be described briefly. In a case where the condition of the recording paper 201 was judged to be the paper sufficiency condition because of the turning on of the photosensor 103 within the time T1, thereafter the printing was started, and subsequently the photosensor 103 turned off, it can be identified that the turning-off of the photosensor 103 was caused by the contact of the detection arm part 119 and the arm contact part 123 as shown in FIGS. 7A and 7B. Thus, based on such a change in the output of the photosensor 103, the paper remaining amount judgment section 226 of the print control section 222 judges that the condition of the recording paper 201 has changed from the paper sufficiency condition to the near end condition, and the near end display is made on the display panel 218.

In a case where the photosensor 103 turned on and thereafter turned off again due to further continuation of the printing, it can be identified that the condition of the recording paper 201 is the paper end condition as shown in FIGS. 8A and 8B. Thus, based on such a change in the output of the photosensor 103, the paper remaining amount judgment section 226 of the print control section 222 judges that the condition of the recording paper 201 has shifted to the paper end condition, and the paper end display is made on the display panel 218. By the above processing, the display indicating the condition of the recording paper 201 can be made based on the change in the output of the photosensor 103 even when the condition of the recording paper 201 changes due to continuation of the printing.

Incidentally, the detection condition for the near end display is designed so that the near end display is made at 60 sheets when thick paper (corresponding to 88-104 gsm (g/m²)) is used, for example. In contrast, in a case where the stored recording paper 201 is regular paper (corresponding to 64-74 gsm), making the near end display on the same condition as the thick paper at the time of the contact of the detection arm part 119 and the arm contact part 123 results in the near end display made when the remaining number of sheets of the recording paper 201 in the sheet feed storage cassette 230 is larger than 60 sheets due to the smaller thickness of the paper.

Since such variations in the remaining number of sheets can occur as above depending on the thickness of the recording paper 201 stored in the sheet feed storage cassette 230, it is necessary to correct the timing of the near end display depending on the thickness of the recording paper 201. FIG. 10 is a diagram showing the relationship between the thickness of the recording paper 201 and a corrective number of sheets used for correcting the timing of the near end display in the first embodiment.

In the first embodiment, the correction of the near end display timing is made by using the corrective numbers of sheets shown in FIG. 10. For example, the corrective number of sheets for the “regular paper” with respect to the “thick paper” is calculated as “24 sheets” based on the following conditions (1) to (3):

thick paper: 60 sheets (0.124 mm×60 sheets=7.4 mm high)  (1)

regular paper: 84 sheets (7.4 mm/0.088 mm=84 sheets)  (2)

near end detection sheet number difference: 84 sheets regarding regular paper−60 sheets regarding thick paper=24 sheets  (3)

Thus, the paper remaining amount judgment section 226 of the print control section 222 has the near end display made on the display panel 218 after the print number counter 223 has counted 24 printed sheets since the reception of a notification that the photosensor 103 is off. Incidentally, also when a setting of a different paper type (relatively thick paper, thin paper) is made, the near end display timing is corrected similarly based on the corrective numbers of sheets shown in FIG. 10.

(1-3) Effect

As described above, in the image forming device 100 according to the first embodiment, combining the photosensor 103 and the rotating paper end sensor lever 102 makes it possible to detect both the paper end condition and the near end condition with only a conventionally existing sensor for the paper end detection, without the need of specially providing a sensor for the near end detection. Accordingly, the production cost of the mechanism for detecting the paper end condition and the near end condition can be reduced.

In the image forming device 100 according to the first embodiment, the timing of the near end display is corrected depending on the thickness of one sheet of the recording paper 201 being used. Accordingly, the near end display can be made at approximately the same remaining number of sheets even when the thickness of the used recording paper 201 is different, and the variations in the remaining number of sheets of the recording paper 201 in the sheet feed storage cassette 230 at the time of making the near end display can be restrained. Consequently, precise near end display can be implemented irrespective of the thickness of the used recording paper 201.

(2) Second Embodiment (2-1) Configuration

A description of an image forming device 100 a according to a second embodiment will be given below exclusively of parts different from those of the image forming device 100 according to the first embodiment. FIG. 11A is a side view showing the general configuration of a sheet feed storage cassette 230 a in the second embodiment, and shows a state where preliminary detection explained later is made. FIG. 11B is a partially enlarged view of a paper remaining amount detection section 200 a in the sheet feed storage cassette 230 a shown in FIG. 11A.

FIG. 12A is a partially enlarged view of the paper remaining amount detection section 200 a in the second embodiment. FIG. 12A shows a state after the preliminary detection and before the near end condition is detected. FIG. 12B is a partially enlarged view of the paper remaining amount detection section 200 a in the second embodiment. FIG. 12B shows a state at a time when the near end condition is detected. FIG. 12C is a partially enlarged view of the paper remaining amount detection section 200 a in the second embodiment. FIG. 12C shows a state at a time when the paper end condition is detected.

As shown in FIGS. 11A and 11B, the image forming device 100 a according to the second embodiment differs from the image forming device 100 according to the first embodiment in having a preliminary detection projection part 118 on the sun gear 107. The preliminary detection projection part 118 is used for correcting the timing of the near end display by estimating the thickness of one sheet of the recording paper 201 stored in the sheet feed storage cassette 230 from the number of sheets of the recording paper 201 on which the printing is performed in a time period of the preliminary detection.

As shown in FIGS. 11A and 11B, the preliminary detection projection part 118 is arranged to the right of the detection projection part 117 of the sun gear 107 in the figures. The preliminary detection projection part 118 has a length around the sun gear 107 corresponding to an angle θ1. In the second embodiment, the height of the projection of the preliminary detection projection part 118 is equal to the height of the projection of the detection projection part 117.

(2-2) Operation

The operation of the image forming device 100 a according to the second embodiment will be described below. The operation from the insertion of the sheet feed storage cassette 230 a into the image forming device 100 a to the ascending of the recording paper setting plate 104 is the same as that of the image forming device 100 according to the first embodiment.

After a certain amount of the printing, as shown in FIGS. 11A and 11B, the preliminary detection projection part 118 comes in contact with the detection arm part 119 due to the rotation of the sun gear 107, the detection arm part 119 and the arm contact part 123 come in contact with each other, and the photosensor 103 turns off. At the same time, the print number counter 223 of the print control section 222 starts the count of the number of printed sheets. At that time, the paper end sensor lever 102 has rotated to a fourth rotational position.

The count of the number of printed sheets is made in the time period in which the sun gear 107 rotates clockwise by the angle θ1. After the sun gear 107 rotates by the angle θ1, the contact of the preliminary detection projection part 118 and the detection arm part 119 is released and the contact of the detection arm part 119 and the arm contact part 123 is also released as shown in FIG. 12A. Since the paper contact part 124 and the recording paper 201 are in contact with each other at that time, the paper end sensor lever 102 rotates by a prescribed angle and the photosensor 103 turns on. The number of printed sheets counted in the aforementioned time is sent to and stored in the paper remaining amount judgment section 226 of the print control section 222.

As the printing is continued further, the detection arm part 119 is raised due to the contact of the detection projection part 117 with the detection arm part 119 as shown in FIG. 12B, the detection arm part 119 and the arm contact part 123 come in contact with each other again, and the photosensor 103 turns off. At that time, the paper remaining amount judgment section 226 of the print control section 222 determines the timing of the near end display based on the number of printed sheets counted earlier.

As the printing is continued further, the contact of the detection projection part 117 and the detection arm part 119 is released as shown in FIG. 12C and the contact of the detection arm part 119 and the arm contact part 123 is also released, and thus the photosensor 103 remains off.

FIG. 13A is a time chart showing an example of the near end detection in the second embodiment and FIG. 13B is a time chart showing another example of the near end detection in the second embodiment. FIGS. 13A and 13B show the timing of the on/off switching of the photosensor 103 corresponding to the timing of the paper end display and the near end display. FIG. 13A shows an example of the time chart in a case where the thickness of the recording paper 201 is 104 gsm, while FIG. 13B shows an example of the time chart in a case where the thickness of the recording paper 201 is 64 gsm.

As mentioned earlier, in the time period of the preliminary detection, the photosensor 103 remains off and thus the number of printed sheets in the time period is counted. As shown in FIG. 13A, if the number C of sheets counted in the time period of the preliminary detection is 60 sheets which is equal to a design value, for example, the near end display is made at the same time as the turning-off of the photosensor 103. Accordingly, the near end display is made when the remaining number of sheets of the recording paper 201 is 60 sheets as shown in FIG. 13A.

In contrast, in a case where the number D of sheets counted in the time period of the preliminary detection is 84 sheets as shown in FIG. 13B, the near end display is made after the printing is performed on 24 sheets (prescribed number of sheets) as the difference between 84 sheets and 60 sheets since the turning-off of the photosensor 103. Accordingly, even in a case where the recording paper 201 is thin (64 gsm), the near end display is made when the remaining number of sheets of the recording paper 201 is 60 sheets as shown in FIG. 13B. As above, by making the above-described correction, it becomes possible to make the near end display when the remaining number of sheets of the recording paper 201 is a constant number (e.g., 60 sheets) irrespective of the thickness of the recording paper 201.

(2-3) Effect

As described above, in the image forming device 100 a according to the second embodiment, a correction value calculated from the difference between the actual number of sheets on which the printing is performed in a certain fixed period (in the time period of the preliminary detection) and the design value is used for determining the timing of the near end display. By making the correction by use of an actual measurement value as above, the preciseness is greatly increased compared to correction made by use of a correction value previously set for each of several paper types, and it becomes possible to make a precise near end display with smaller variations in the remaining number of sheets.

Further, with the image forming device 100 a according to the second embodiment, effects similar to those of the image forming device 100 according to the first embodiment can be achieved.

(3) Third Embodiment (3-1) Configuration

A description of an image forming device 100 b according to a third embodiment will be given below exclusively of parts different from those of the image forming device 100 a according to the second embodiment. FIG. 14A is an enlarged view showing the general configuration of a paper remaining amount detection section 200 b in the third embodiment, and shows a state at a time when the paper sufficiency condition is detected. FIG. 14B is an enlarged view showing the general configuration of the paper remaining amount detection section 200 b in the third embodiment, and shows a state at a time of the preliminary detection.

FIG. 14C is an enlarged view showing the general configuration of the paper remaining amount detection section 200 b in the third embodiment, and shows a state after the preliminary detection and before detecting the near end condition. FIG. 14D is an enlarged view showing the general configuration of the paper remaining amount detection section 200 b in the third embodiment, and shows a state at a time when the near end condition is detected. FIG. 14E is an enlarged view showing the general configuration of the paper remaining amount detection section 200 b in the third embodiment, and shows a state at a time when the paper end condition is detected.

FIG. 15 is a flowchart showing an operation for near end detection restoration in the third embodiment. FIG. 16 is a table showing the relationship between an output of a density sensor 135 and a display on the display panel 218 in the third embodiment.

The image forming device 100 b according to the third embodiment differs from the image forming device 100 a according to the second embodiment in including the density sensor 135 instead of the photosensor 103. Further, the image forming device 100 b according to the third embodiment differs from the image forming device 100 a according to the second embodiment in including a first density sensor reflective part 130 as a second reflective part, a second density sensor reflective part 131 as a first reflective part, a third density sensor reflective part 132 as a third reflective part and a fourth density sensor reflective part 137 instead of the photosensor transmissive part 120 a, the first photosensor light blocking part 120 b and the second photosensor light blocking part 120 c.

Furthermore, the image forming device 100 b according to the third embodiment differs from the image forming device 100 a according to the second embodiment in that the height of the preliminary detection projection part 118 of the sun gear 107 in the sheet feed storage cassette 230 is smaller than the height of the detection projection part 117 by hl and the photosensor optical axis 133 is replaced with a density sensor detecting position 136.

As shown in FIG. 14A to FIG. 14E, the paper end sensor lever 102 of the image forming device 100 b according to the third embodiment has the first to fourth density sensor reflective parts 130, 131, 132 and 137. Further, the density sensor 135 has the density sensor detecting position 136. The paper end sensor lever 102 rotates around the shaft 102 a and thereby reflects light emitted from the density sensor 135 at the positions of the first to fourth density sensor reflective parts. The intensity of the reflected light is detected at the density sensor detecting position 136.

The first density sensor reflective part 130 is arranged at the rightmost position among the density sensor reflective parts. The intensity of the reflected light reflected by the first density sensor reflective part 130 is the second highest among the first to fourth density sensor reflective parts and is detected at the density sensor detecting position 136. Then Middle-High (Mid-H) is outputted by the density sensor 135 (see FIG. 16). The first density sensor reflective part 130 is used to detect the near end condition.

The second density sensor reflective part 131 is arranged at the leftmost position among the density sensor reflective parts. The intensity of the reflected light reflected by the second density sensor reflective part 131 is the lowest among the density sensor reflective parts and Low is outputted by the density sensor 135 (see FIG. 16). The second density sensor reflective part 131 is used to detect the paper end condition.

The third density sensor reflective part 132 is arranged at the third position from the right among the density sensor reflective parts. The intensity of the reflected light reflected by the third density sensor reflective part 132 is the highest among the density sensor reflective parts and High is outputted by the density sensor 135 (see FIG. 16). The third density sensor reflective part 132 is used to detect the paper sufficiency condition.

The fourth density sensor reflective part 137 is arranged at the second position from the right among the density sensor reflective parts. The intensity of the reflected light reflected by the fourth density sensor reflective part 137 is the third highest among the density sensor reflective parts and Middle-Low (Mid-L) is outputted by the density sensor 135 (see FIG. 16). The fourth density sensor reflective part 137 is used to make the preliminary detection.

(3-2) Detecting Operation in Normal Times

The operation of the image forming device 100 b according to the third embodiment will be described below with reference to FIGS. 14A to 14E. The operation from the insertion of the sheet feed storage cassette 230 into the image forming device 100 b to the ascending of the recording paper setting plate 104 is the same as that of the image forming device 100 a according to the second embodiment and starts from the state shown in FIG. 14A.

As shown in FIG. 14B, after a certain amount of the printing, the preliminary detection projection part 118 comes in contact with the detection arm part 119 due to the rotation of the sun gear 107, the detection arm part 119 also comes in contact with the arm contact part 123, and the fourth density sensor reflective part 137 of the paper end sensor lever 102 moves to a position coinciding with the density sensor detecting position 136.

At that time, the density sensor 135 receives the reflected light from the density sensor reflective part 137 at the density sensor detecting position 136 and the output Middle-Low (Mid-L) is acquired, while the print number counter 223 of the print control section 222 starts the count of the number of printed sheets at the same time.

As shown in FIG. 14C, as the sun gear 107 rotates further, the contact of the detection arm part 119 and the arm contact part 123 is released and the third density sensor reflective part 132 of the paper end sensor lever 102 moves to the position coinciding with the density sensor detecting position 136.

At that time, the density sensor 135 receives the reflected light from the third density sensor reflective part 132 at the density sensor detecting position 136, the count of the number of printed sheets is stopped due to the acquisition of the output High, and the counted number of printed sheets is sent to and stored in the paper remaining amount judgment section 226 of the print control section 222.

As shown in FIG. 14D, as the printing is continued further, the detection projection part 117 and the detection arm part 119 come in contact with each other and the first density sensor reflective part 130 of the paper end sensor lever 102 moves to the position coinciding with the density sensor detecting position 136.

At that time, the density sensor 135 receives the reflected light from the first density sensor reflective part 130 at the density sensor detecting position 136 and the output Middle-High (Mid-H) is acquired, while a paper near end notification is issued from the paper remaining amount judgment section 226 of the print control section 222 at the same time and the near end display is made on the display panel 218.

As shown in FIG. 14E, as the printing is continued further, the contact is lost between the recording paper 201 and the paper contact part 124, and the second density sensor reflective part 131 of the paper end sensor lever 102 moves to the position coinciding with the density sensor detecting position 136.

At that time, the density sensor 135 receives the reflected light from the second density sensor reflective part 131 at the density sensor detecting position 136, the output Low is acquired, the paper remaining amount judgment section 226 of the print control section 222 judges that the paper is in the paper end condition, and the paper end display is made on the display panel 218. The flow from the setting of the recording paper 201 to the paper end display in normal printing is as described above.

(3-3) Operation at Power Shutdown

Next, an operation for recognizing again the amount of the recording paper 201 in the sheet feed storage cassette 230 and the position of the paper end sensor lever 102, in a case where the power of the image forming device 100 b with some recording paper 201 remaining therein is shut down due to some trouble and thereafter turned on again and the information stored in the paper remaining amount judgment section 226 of the print control section 222 is lost, will be described below with reference to FIG. 15.

As shown in FIG. 15, in step S11, an output check of the density sensor 135 “Is sensor output Low?” is made by the print control section 222. If the sensor output is Low (YES in the step S11), it is judged that the density sensor detecting position 136 and the second density sensor reflective part 131 have coincided with each other, the process advances to a next step S12, and the paper end display is made on the display panel 218.

If the sensor output is not Low (NO in the step S11), the process advances to a next step S13 and an output check of the density sensor 135 “Is sensor output High?” is made.

If the output is High (YES in the step S13), it is judged that the density sensor detecting position 136 and the third density sensor reflective part 132 have coincided with each other, the process advances to a next step S14, and the paper remaining amount judgment section 226 has the paper sufficiency (printable) display made on the display panel 218. Subsequently, the process advances to step S15 and the recording paper 201 is fed without change. Thereafter, in the next step S16, whether or not the sensor output is still High also after a time T3 is checked.

If the sensor output is still High also after the time T3 (YES in the step S16), the process advances to a next step S17 and the paper sufficiency display on the display panel 218 is continued since the density sensor detecting position 136 and the third density sensor reflective part 132 are coinciding with each other.

If the sensor output is not High after the time T3 (NO in the step S16), the process advances to a next step S18 and an output check of the density sensor 135 “Is sensor output Mid-L?” is made. If the sensor output is Mid-L (YES in the step S18), it is judged that the density sensor detecting position 136 and the fourth density sensor reflective part 137 have coincided with each other, the operation mode shifts to a preliminary detection mode in which the preliminary detection is made in a next step S19, and the count of the number of printed sheets is started by the print number counter 223.

If the sensor output is not Mid-L (NO in the step S18), it is judged that the density sensor detecting position 136 and the first density sensor reflective part 130 have coincided with each other and the near end display is made on the display panel 218 in a next step S20.

Returning to the step S13 “Is sensor output High?”, if the output is not High (NO in the step S13), the process advances to a next step S21 and a check “Is sensor output Mid-L?” is made. If the sensor output is Mid-L (YES in the step S21), it is judged that the density sensor detecting position 136 and the fourth density sensor reflective part 137 have coincided with each other, the operation mode shifts to the preliminary detection mode in which the preliminary detection is made in a next step S22, and the count of the number of printed sheets is started by the print number counter 223.

If the sensor output is not Mid-L (NO in the step S21), the process advances to a next step S23, it is judged that the density sensor detecting position 136 and the first density sensor reflective part 130 have coincided with each other, and the near end display is made on the display panel 218.

(3-4) Effect

In the image forming devices 100 and 100 a according to the first and second embodiments described earlier, the remaining amount of the paper is judged based on two types of indication, on and off, by the photosensor 103 and there are two conditions, the paper end condition and the near end condition, when the photosensor 103 is off, and thus physical discrimination between the paper end condition and the near end condition cannot be made in a case where an unexpected shutdown of the device power occurred and the power is restored. Therefore, in such a case where an unexpected device power shutdown occurred and the power is restored, a problem arises in that the near end detection function cannot be restored unless the sheet feed storage cassette 230 is once drawn out from the device and reinserted into the device.

In contrast, with the image forming device 100 b according to the third embodiment, it becomes possible to physically and instantaneously judge whether the remaining amount of paper is in the paper end condition, in the near end condition, in the paper sufficiency condition or in the preliminary detection condition in which the preliminary detection is made based on the output of the density sensor 135. Accordingly, effect is achieved in that the user is relieved of the work of reinserting the sheet feed storage cassette 230 into the device and the near end detection function can be restarted automatically.

Further, with the image forming device 100 b according to the third embodiment, effects similar to those of the image forming devices 100 and 100 a according to the first and second embodiments can be achieved.

(4) Description of Forms of Use

While examples of applying the present invention to a paper feed device of an electrophotographic printer have been described in the above embodiments, the present invention is applicable to any type of image forming devices that include a sheet feed storage cassette and a paper end sensor, and form an image on recording paper by using various printing methods, such as copiers, facsimile machines, printers and MFPs (multifunction printers).

In the above embodiments, messages regarding the paper end condition and the near end condition of the recording paper 201 are displayed by using the display panel 218 as a display section. However, the method of indication is not limited to such examples and it is possible, for example, to provide the device with an LED or the like as the display section and to indicate the paper end condition and the near end condition by using the color, the pattern or the like of light emitted from the LED.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of following claims. 

What is claimed is:
 1. A medium detection mechanism comprising: a medium setting part in which media are set; a rotating member having a rotational central shaft, the rotating member being configured to rotate around the rotational central shaft depending on an amount of the media set in the medium setting part; a detection sensor that detects the rotation of the rotating member; a display section that displays a condition of the medium detection mechanism; and a control section that controls the display section, wherein the rotating member includes a first arm part for detecting a first condition in which there are no media set in the medium setting part and a second arm part for detecting a second condition in which the amount of the media set in the medium setting part is smaller than a prescribed amount, and the control section makes a first display indicating that there are no media set in the medium setting part on the display section when the media are judged to be in the first condition based on result of the detection by the detection sensor and makes a second display indicating that the amount of the media set in the medium setting part is smaller than the prescribed amount on the display section when the media are judged to be in the second condition based on the result of the detection by the detection sensor.
 2. The medium detection mechanism according to claim 1, wherein the rotating member rotates to a first rotational position when the media are in the first condition and rotates to a second rotational position when the media are in the second condition.
 3. The medium detection mechanism according to claim 2, wherein the first arm part is used for detecting a third condition in which the amount of the media set in the medium setting part is not smaller than the prescribed amount, and the control section makes a third display indicating that the amount of the media in the medium setting part is not smaller than the prescribed amount on the display section when the media are judged to be in the third condition.
 4. The medium detection mechanism according to claim 3, wherein the rotating member rotates to a third rotational position when the media are in the third condition.
 5. The medium detection mechanism according to claim 4, wherein the detection sensor includes a photosensor having a light emission part and a light reception part, the rotating member further includes a light blocking part that blocks light emitted from the light emission part and a light transmissive part that transmits the light emitted from the light emission part, the light blocking part rotates together with the rotation of the rotating member so that the light is blocked by the light blocking part in a state in which the rotating member has rotated to the first or second rotational position, and the detection sensor detects that the rotating member has rotated to the first or second rotational position based on turning-off of the photosensor caused by the blockage of the light.
 6. The medium detection mechanism according to claim 5, wherein the light transmissive part rotates together with the rotation of the rotating member so that the light is transmitted by the light transmissive part in a state in which the rotating member has rotated to the third rotational position, and the detection sensor detects that the rotating member has rotated to the third rotational position based on turning-on of the photosensor caused by the transmitted light.
 7. The medium detection mechanism according to claim 6, further comprising a medium conveyance part that comes in contact with a top layer medium among the media set in the medium setting part and an elastic part that biases the medium setting part upward, wherein the medium setting part ascends further by the elastic part with decrease in the amount of the media set in the medium setting part.
 8. The medium detection mechanism according to claim 7, wherein the medium setting part starts ascending by the elastic part when the medium setting part is set in an image forming device and stops ascending when the top layer medium comes in contact with the medium conveyance part, and the photosensor turns on when the top layer medium comes in contact with the medium conveyance part.
 9. The medium detection mechanism according to claim 8, further comprising a time measurement section that measures a measurement time from the start of the ascending of the medium setting part to the turning-on of the photosensor, wherein the control section judges that the media are in the third condition when the measurement time is not longer than a predetermined first time.
 10. The medium detection mechanism according to claim 9, wherein the control section judges that the media are in the second condition, when the measurement time is longer than the first time and not longer than a second time longer than the first time and the photosensor turns off after elapse of the measurement time.
 11. The medium detection mechanism according to claim 10, wherein the control section judges that the media are in the first condition when the measurement time is longer than the second time.
 12. The medium detection mechanism according to claim 4, further comprising a print number measurement section that counts a number of printed sheets in a prescribed time, wherein the control section makes the second display on the display section after printing on a prescribed number of sheets is counted by the print number measurement section since the media are judged to be in the second condition.
 13. The medium detection mechanism according to claim 12, wherein the prescribed number of sheets is smaller with increase in a thickness of one sheet of the media and larger with decrease in the thickness of one sheet of the media.
 14. The medium detection mechanism according to claim 12, further comprising a projection part that moves in conjunction with ascending of the medium setting part and makes the rotating member rotate to a fourth rotational position, wherein the control section determines the prescribed number of sheets based on a difference between the number of printed sheets measured in a time period in which the rotating member rotates to the fourth rotational position and a design value.
 15. The medium detection mechanism according to claim 4, wherein the detection sensor includes a light emission part and a density sensor that measures intensity of reflected light of light emitted from the light emission part, the rotating member further includes first to third reflecting parts that rotate together with the rotation of the rotating member, and intensities of the light reflected by the first to third reflecting parts are different from each other, and the detection sensor detects the rotation of the rotating member based on the intensity of the reflected light measured by the density sensor.
 16. The medium detection mechanism according to claim 15, wherein the detection sensor detects that the rotating member has rotated to the first rotational position when the intensity of the reflected light measured by the density sensor is the intensity of the reflected light reflected by the first reflecting part, the detection sensor detects that the rotating member has rotated to the second rotational position when the intensity of the reflected light measured by the density sensor is the intensity of the reflected light reflected by the second reflecting part, and the detection sensor detects that the rotating member has rotated to the third rotational position when the intensity of the reflected light measured by the density sensor is the intensity of the reflected light reflected by the third reflecting part.
 17. The medium detection mechanism according to claim 2, further comprising a gear part that rotates together with ascending of the medium setting part, wherein a projection part is formed on a part of a periphery of the gear part, and the projection part rotates together with the rotation of the gear part, and the rotated projection part presses the second arm part of the rotating member via an intermediating member and thereby causes the rotating member to rotate to the second rotational position.
 18. An image forming device comprising the medium detection mechanism according to claim
 1. 